We propose an exploratory project to create peptide MHC II tetramers that will advance insight into the immunity to endemic mycoses and the biology of long-lived memory among IL-17 producing CD4+ T cells. Ag- specific T cells that enter the pool of long-lived memory cells represent the cellular basis of immunological memory, which is the underpinning of vaccine- and protective-immunity. An understanding of T cells that persist in this pool is needed for the rationale design of vaccines. There are differing views about the longevity of T helper 17 cells. Amid this debate, there's a knowledge gap about CD4+ T cells that enter the memory pool after fungal vaccination, and whether the cells retain the ability to produce IL-17. This knowledge gap is a barrier to disease prevention strategies since Th17 cells promote vaccine immunity to fungi. We hypothesize that Ag-specific CD4+ T cells that protect against dimorphic fungi - Blastomyces, Histoplasma, and Coccidioides - enter the memory pool and retain the ability long-term to produce IL-17 on re-exposure to the pathogen. We'll test our hypothesis by using a novel TCR transgenic mouse to decipher the identity of a dominant, protective Ag conserved in dimorphic fungi, and introduce the antigen's T cell epitope into peptide-MHC (pMHC) tetramers to track the evolution, persistence, phenotype and function of endogenous Ag-specific CD4+ T cells in vivo under physiological conditions after fungal vaccination and re-exposure in the lung. Our aims are to: 1) Identify the shared protective fungal Ag and epitope and create and validate peptide MHC tetramers. We will identify, clone and express the fungal Ag recognized by vaccine induced CD4+ T cells that mediate protective immunity to endemic mycoses. Our preliminary data point strongly toward calnexin. We'll deduce the peptide epitope of the Ag recognized by the class II MHC of BL/6 mice and synthesize and validate pMHC tetramers to let us monitor and track endogenous epitope specific CD4+ T cells under physiological conditions. 2) Define the persistence and phenotype of vaccine-induced anti-fungal T17 cells using pMHC tetramers. We will use pMHC tetramers to define the size of the endogenous pool of epitope-specific CD4+ T cells in nave BL/6 mice. In vaccinated mice, we will use pMHC tetramers to track the long-term fate, persistence and phenotype of memory CD4+ T cells that mediate resistance to the mycoses, with an emphasis on clarifying the extent to which Th17 cells persist after vaccination to blastomycosis, histoplasmosis, and coccidioidomycosis. Our work will yield new insight into the phenotype and function of CD4+ T cells that confer protective immunity to the endemic mycoses, and especially the persistence of IL-17 producing cells over an extended period. The results will be broadly significant and impactful for those working in Mycology & Immunology.